Frequency Conversion

[curious555]

I just want to convert the frequency of any input audio into ultrasonic sound ( in the rate of 25 Khz) . Please help me with a schematic ..

Does tweeter can produce the sound in the order of 25 khz ???

 

[duke37]

Please give more details.
Do you wish to give out an ultrasonic beep when any sound is input?
Do you wish to preserve the amplitude and frequency information when shifted to 25kHz.

A description of the reason behind this would help.

Frequency shifts are the way superhet radio receivers work. The circuits are well known but are not simple for a beginner.
Very low power transmitters are used to activate very old medium wave receivers, one of these could be modified to give an output at 25kHz or so, 'pantry transmitter'.

There is a thread running to convert bat squeaks down into the audio range, I have not been following this.

 

[Raven Luni]

A heterodyne is what you're after. Amplitude modulation of a signal will give you 2 outputs which are the sum and the difference of the original frequencies (this is why you have 2 side bands in an AM signal). If youre aiming as low as 25Khz you will have to do this twice - one upshift (to a much higher intermetiate frequency) and one downshift. Both times, you will have to filter out the unwanted half of the signal.

As for bat detectors, I haven't built any heterodyne ones yet - only frequency division (completely different method which only works downwards)